This invention relates generally to control and supervision of electromechanical devices which have internal parts which are capable of moving or oscillating relative to one another. This invention relates specifically to supervisory control and indicating systems for turbine driven, high power, alternating current, synchronous generator systems which may be subjected to torsional oscillations in the shaft thereof.
It has been found that in long line electrical transmission systems of the type where the electrical generators are driven from power sources such as steam turbines, multiple rotating masses may be present on a single shaft. As an example, the rotating mass of one or more turbines and the rotating mass of an exciter for an AC generator as well as the rotating mass of the generator rotor may be present on the same shaft. Because of the mechanical properties of the various parts of the rotating system, torsional oscillations along the shaft may be possible at any time between any combination of the masses. If these torsional oscillations were to become large and undamped they could cause shaft breakage. It has been found in certain applications that such undamped torsional oscillations may exist because of the electrical properties of the AC synchronous generator electrical system. As an example, when long transmission lines are required for the delivery of energy to an electrical grid network or load the inductive effect of the long transmission lines may require series capacitive compensation. However, the effect of the compensating capacitors connected in series circuit relationship with the inductance of the long transmission line may tend to cause certain resonant frequencies to exist in the output electrical circuit of the AC generator. These resonant frequencies may be reflected through the magnetic coupling between the stator and rotor of the synchronous generator to the mechanically rotating shaft. If the previously described electrical resonant frequency occurs at a critical mechanical resonant frequency between any of the masses of the turbine-generator system, reinforced undamped torsional oscillation may occur in the shaft which may be of sufficient magnitude to break the shaft. Apparatus and methods for solving this problem have been proposed in the previously described copending application Ser. No. 466,318 and in U.S. Pat. No. 3,662,251 issued May 9, 1972 to O. J. M. Smith entitled "Method and System for Measuring Acceleration and Velocity." This latter patent is related to the sensing of the oscillation of the shaft and the operation thereupon. A similar method and apparatus is described in U.S. Pat. No. 3,662,252 issued May 9, 1972 to O. J. M. Smith and entitled "Tachometer and Method of Obtaining a Signal Indicative of Alternating Shaft Speed." Apparatus for measuring angular displacement are taught in U.S. Pat. No. 3,208,274 issued to R. C. Rosaler on Sept. 28, 1965 and U.S. Pat. No. 3,505,865 issued to G. A. Kihlberg et al on Apr. 14, 1970. Similarly, apparatuses for measuring torque are taught in U.S. Pat. Nos. 2,675,700 issued to T. C. Van Dergrift et al on Apr. 20, 1954; 2,634,604 issued to L. F. Hope on Apr. 14, 1953; and 3,194,065 and issued to M. W. Wilson on July 13, 1965; and likewise a slip indicator is taught in U.S. Pat. No. 2,387,901 issued to S. A. Haverstick on Oct. 30, 1945. Each of the latter aforementioned patents teaches methods and/or apparatus for determining various parameters associated with rotating electrical machinery. It would be advantageous if an apparatus and a method could be developed for utilizing a relatively easily measured parameter of a rotating electro-mechanical system in conjunction with an analog computer model of that system to thereby provide information about other portions of the electro-mechanical system by utilizing the information readily available at easily accessible parts of the model.